1. Field of the Invention
The present invention relates generally to packaging for photonic devices and particularly to packaging for 2-, 3- and multiple-port optical devices such as WDM filters, and various crystal-based devices.
2. Technical Background
A typical WDM module includes numerous optical circuits arranged in parallel and in series to address a large number of channels. Each circuit is formed by a number of collimating and/or filtering-collimating assemblies, each including a 3-port filtering package that includes optical fibers inserted and bonded into glass ferrules to produce fiber-ferrule “pigtails,” collimating lenses, and a spectral shaping thin film optical filter. In a typical 3-port package, the collimating lens receives the light emitted from the input fiber, collimates this light into parallel rays, and transmits them to the filter. The filter splits the collimated light into two separate beams, a transmitted beam and a reflected beam. The transmitted beam is then coupled into an output collimating assembly. The reflected beam is reflected and coupled into the adjacent reflective fiber.
To provide these operations between the filter and collimating assemblies, a tip-tilt or a translational active alignment of collimating and filter assemblies is used. The interrelationships between the assemblies that reflect the achieved optimum alignment is then locked in place using various bonding, soldering or welding encapsulation techniques. The filter price and the packaging costs are two dominating factors affecting the cost of the 3-port packages and WDM modules. Typical 3-port packages have used active alignment, reciprocally duplicating adhesive bonding and soldering encapsulation techniques involving several structural sub-components, for example, a pair of insulating tubes and several metal protective units per package. All this makes manufacturing of the packages time-consuming and expensive.
Examples of attempts to improve and simplify 3-port filtering packages, their assembly and encapsulation are found in, for example, U.S. Pat. No. 6,282,339 and U.S. Pat. No. 6,185,347, which show packages made from adhesively bonded and interrelated glass components and tubular glass holder units. With these designs the necessity of the soldering or welding encapsulation involving structural metal units is, therefore, eliminated from the packaging process. However, these packaging approaches still exhibit certain limitations. They require a great deal of active alignment, and the precision mechanical design of the butt joints. The rheology and the time-dependent degradation of epoxy adhesives located within the optical path of the package require different adhesive materials in various bonds used in the package. In assembly, a previously achieved precise active alignment can be easily harmed due to heat-cure assisted polymerization and the accompanying it thermal shrinkage in a subsequent step. In-situ heat cure fixing the active alignment steps requires, therefore, an alignment station that is able to retain the interrelationships between the aligned assemblies inside the package at elevated temperatures. Thus, in spite of the simplifications in the package design and manufacturing suggested in these references, the packaging process remains time-consuming and expensive. Therefore, a need still exists in the design and manufacturing of low-cost, viable, and reliable filter- or crystal-based packages that will be able to overcome the difficulties discussed above.
Thus, it would be desirable to have a filtering assembly for two-, three-, and higher port-count temperature-compensated optical filtering packages, which is simpler in construction, inexpensive in materials and manufacturing, and reliable in operations.